1. Field of the Invention
The invention relates to a digital interface device and a digital interface method, which multiplex a plurality of data upon each other so as to be able to execute synchronous transfer.
2. Related Art Statement
In recent years, digital processing of an image has been considered. Various digital processing devices and methods have also been considered regarding a magnetic recording and reproducing apparatus of digital image data. For example, in a conference discussing a digital VTR (video tape recorder) for public welfare in Japan, digital signal standards were decided, such is an SD standard for compressing an NTSC signal, a PAL signal or the like and for recording the same, and an ED standard for compressing a base band signal of an HDTV (High Definition TV) and for recording the same. The digital VTR for public welfare which corresponds to these standards has been widely sold.
Generally, when a video signal is digitalized, the amount of information contained in the signal greatly increases, and it becomes difficult to execute transmission, recording or the like without compressing the information, in view of a communication rate, expense or the cost. For this reason, in the transmission and recording of the digital video signal, an image compression technique is essential, and various kinds of standardizing proposals have been considered in recent years. As one example, for animation, an MPEG (Moving Picture Experts Group) system has been standardized.
Particularly, an MPEG 2 system has been widely used as a standardization system for image compression, and has been adopted in digital broadcasting in the U.S.A. and Europe. A decoder which corresponds to the MPEG standard has also been sold. The decoder is supplied as an MPEG decode board, and is loaded onto a computer or the like.
In keeping with growth of the image compression technique, development of digital imaging equipment has also progressed. Not only the digital VTR, but also a decoder for digital broadcasting (digital set top box), and a digital video disc player have been sold.
The advantages to digitization include reduction in depletion or deterioration in the transmission and recording, and obtaining a reproduced image of high quality. If these characteristics are considered, all digital imaging units should be arranged to have a digital interface which not only enables analog input and output similarly to conventional equipment, but also which enables input and output of the digital signal. The digital interface may also treat the image data merely as digital data. Thus making it possible to connect equipment having the digital interface to a computer, not-withstanding the fact that the digital and analog units may be connected to each other to transmit the data.
FIG. 11 is a block diagram showing the related technique of a digital interface device which is used in a digital VTR.
The block diagram in FIG. 11 applies to a VTR which uses the standard of the above-described conference of the digital VTR for public welfare and is arranged to record the standard television image after it is digitalized so that an amount of data has been compressed to about 1/5 to 1/6. In the 6 mm digital tape format adopted in the igital VTR, it is also possible to record digital data other than the image. Accordingly, the recording capacity of a 6 mm digital tape is much larger than that of a DAT (digital audio tape), or a tape recorder in the 8 mm format. Since the recording area of video data in a single magnetic tape has a recording capacity of 50 Giga bytes, application as a high capacity digital data streamer is expected in the future.
An analog image signal is input to input terminal 1. This analog image signal is converted to a digital signal by an A/D transducer 2. The A/D transducer 2 changes sampling frequency with respect to an intensity or luminance signal Y and color-difference signals Cr and Cb, to output a component signal of 4:1:1 to a compression circuit 3. The compression circuit 3 compresses the component signal, which is inputted by DCT processing, quantization processing and variable-length coding processing. Thus, an input analog image signal in which a transmission rate is 125 Mbps is converted to 19 Mbps and is supplied to a correction or revision coding circuit 4. The revision coding circuit 4 adds an error correction code to the inputted compression data. An output rate of the revision coding circuit 4 is 25 Mbps. A modulation circuit 5 modulates an output from the revision coding circuit 4 to a code which is suitable for magnetic recording, to give the same to an unshown head through an amplifier 6, to thereby magnetically record the same onto a tape 7.
Meanwhile, in a reproducing system, a reproducing signal which is reproduced from the tape 7 by the unshown head is supplied to an equalization detection modulation circuit 9 through an amplifier 8. By the equalization detection modulation circuit 9, the reproduced signal is quantized in waveform and is modulated. The reproduced signal is corrected in error and is given to an extension circuit 11 by a revision decoding circuit 10. The extension circuit 11 extends reproduced data by variable-length decoding processing, inverse quantization processing and inverse DCT processing, to give the same to a D/A transducer 12. The D/A transducer 12 returns the digital signal to an analog signal to output the same through an output terminal 13.
Moreover, in the digital VTR in FIG. 11, it is also possible to record another digital data other than the image data. Specifically, the digital data supplied at terminal 15 passes to the revision coding circuit 4 through a digital I/F (interface) 14. An error revision code is added to the digital data by the revision coding circuit 4, the data is modulated by a modulation circuit 5 and, thereafter, is recorded onto the tape 7. Furthermore, upon reproduction, the digital data from the revision decoding circuit 10 are outputted from the terminal 15 through the digital I/F 14. Since the digital I/F 14 executes transfer of the data not through the compression circuit 3 and the extension circuit 11, no image deterioration or degradation is caused by compression or extension. In this configuration, the input and output transfer rate of the digital I/F 14 is 25 Mbps.
FIGS. 12 to 14 are explanatory views for describing the recording format of the tape 7.
FIG. 12 shows a recording track which is formed on the tape 7, while FIG. 13 shows each data region of one (1) track. As shown in FIGS. 12 and 13, each recording track has a plurality of regions, which correspond to the kinds of data, that is, an ITI, an audio region, a video region and a sub-code region. These regions are successively arranged from a lower end of the tape 7 toward an upper end thereof. Further, gaps G1 to G3 are provided respectively between these regions. By trace of the head, the ITI, the audio region, the video region and the sub-code region are successively recorded and reproduced.
The arrangement is such that, in an SD format of the digital VTR for public welfare, data are recorded onto each track with a one (1) sink block serving as a recording unit. FIG. 14 shows a data arrangement of the sink block in the video region in the one (1) track. As shown in FIG. 14, each sink block is a length of 90 bytes. A synchronous signal (SYNC) of two (2) bytes is arranged at the head, and an ID of three (3) bytes is subsequently provided. Data of 77 bytes are subsequently arranged. Lastly, a parity which consists of an inner code and an outer code is arranged. An outer code for error revision is arranged in one hundred and fifty seventh to one hundred and sixty seventh sink blocks with respect to longitudinal data in FIG. 14, while an inner code for error revision is arranged in eighty second to eighty ninth bytes of nineteenth to one hundred and sixty seventh sink blocks with respect to lateral data.
FIG. 15 is a block diagram showing a related technique of the digital interface device which is used in a case where two digital VTRs 31 and 32 are connected to each other.
Audio and video processing circuits 33 and 34 correspond to the A/D transducer 2, the D/A transducer 12, the compression circuit 3 and the extension circuit 11 in FIG. 11. The audio and video processing circuits 33 and 34 compress audio and video data to output the same, and extend inputted compression data to output audio data and video data. Error revision circuits 35 and 36 correspond respectively to the revision coding circuit 4 and the revision decoding circuit 10 in FIG. 11. The error revision circuits 35 and 36 add error revision codes to the outputs from the audio and video processing circuits 33 and 34, and revise in error the reproduced signal from the magnetic tape to output the same to the audio and video processing circuits 33 and 34.
Digital I/Fs 37 and 38 correspond to the digital I/F 14 in FIG. 11, and execute conversion between the recording format and the transmission format of the magnetic tape. The video data are recorded onto a video region of one hundred and thirty five sink blocks per one (1) track (refer to FIG. 14), and the audio data are recorded onto the audio region of nine (9) sink blocks. The digital I/F 37 and 38 are so arranged as to make one (1) sink block to one (1) packet, and to convert one (1) track to a unit of one hundred and fifty (150) packets to execute input and output of the data in 150 packets.
FIG. 16 shows the packet data corresponding to one (1) track. As shown in FIG. 16, a header packet HO is arranged at the head of one hundred and fifty (150) packets. Subsequently, two sub-code packets SC0 and SC1 and three video auxiliary packets VA0 to VA2 are arranged. Subsequently, nine (9) audio packets A0 to A8 corresponding to nine (9) sink blocks and one hundred and thirty five (135) video packets V0 to V134 corresponding to one hundred and thirty five (135) sink blocks are arranged.
FIG. 17 shows a data structure of an output from the digital I/Fs 37 and 38. A block diagram in FIG. 17 corresponds to the packet in FIG. 16. Specifically, a block 0 to a block 149 correspond to data of one hundred and fifty (150) packets of one (1) track. As shown in FIG. 17, in each block, an ID is arranged at the head, and various kinds of data are subsequently arranged. A header, a sub-code, video auxiliary data and audio and video data, for one (1) track are transmitted by the block 0 to the block 149. The one (1) frame is restored by the data of n track.
In this manner, the data transmission by the digital I/Fs 37 and 38 is executed in a unit of packet. In the digital interface device, in order to enable data transfer between all digital image equipment and computers, it has been considered to adopt a unified interface system. Specifically, to make communication possible not only between the digital image equipment, but also in a computer system, it has been considered to adopt the standard of SCSC or RS232. However, the transmission rates of SCSI and RS232 are extremely low, and it is impossible to transmit image data at rates equal to or more than several Mbps. Furthermore, the image data are different from the computer data, and must be transmitted (hereinafter referred to as "synchronous transmission") at real time and at constant periods of time. These interface systems therefore cannot be adopted for image transmission.
In view of the above, in the conference of the digital VTR and in section R4.1 of E1A from the conference of ATV (Advanced TV) decoder of U.S.A., a high-speed interface system which is suited to the image data has been considered. Particularly, attention is paid to P1394 which has the function of isochronous transfer (hereinafter also referred to as "synchronous transfer"), as a post SCSI.
FIG. 18 and FIGS. 19A.about.19E are explanatory views for describing the interface system of P1394 Which is capable of such synchronous transfer and multiplex transfer of a plurality of channels.
Regarding P1394, the contents thereof are described in detail on pages 152-163 of the article (Literature 1) "Comparison of New Three Interfaces which search for a Design Idea of Post SCSI" of Nikkei Electronics 1994. 7.4 (No. 612). As published on and subsequent to page 161 of the article, P1394 is based on an interface for a computer. However, in view of the fact that it is characterized as to be "provided with the isochronous transfer function for multi-media", P1349 is more effective for image data than the other interface systems.
Moreover, in P1394, as described on and subsequent to page 162 of Literature 1, multi-channeling is possible. FIGS. 19A-19E show an example in which a bus corresponding to P1394 (hereinafter referred to as "P1394 bus") is utilized to transmit data of two (2) channels including channels 1 and 2 (CH1 and CH2). P1394 can adopt topologies in the form of a daisy chain and in the form of a tree. FIG. 18 shows an example in which a plurality of devices A to D are connected to each other in the form a daisy chain through a P1394 cable 40 that is the P1394 bus. In this connection, the devices A to D may be digital VTRs.
FIGS. 19A-19E show an example wherein data are transmitted to the device C from the device A, and the data are transmitted to the device D from the device B. For example, it is assumed that a dubbing output from the device A is recorded in dubbing by the device C, and a dubbing output from the device B is recorded in dubbing by the device D. In P1394, the data are transferred at the isochronous cycle every 125 .mu.s.
FIG. 19A shows a video stream of the dubbing output from the device A. The dubbing output is transferred every isochronous cycle. Moreover, FIG. 19C shows a video stream of the dubbing output from the device B. The dubbing output is also transferred every isochronous cycle. A plurality of channels are allocated to the isochronous cycle. A channel number which indicates by any of channels the output is transferred is inserted into the packets which are outputted by the devices A and B. It is indicated in FIG. 19E that the output packet of the device A is transmitted by the channel 1 (ch1), and the output packet of the device B is transmitted by the channel 2 (ch2).
Furthermore, the devices A and B output commands shown respectively in FIGS. 19B and 19D, through a P1394 cable. These video streams and commands are multiplexed upon each other every isochronous cycle, as shown in FIG. 19E, and are transferred by the P1394 cable 40. In this connection, asynchronous data such as a command or the like are multiplexed onto gaps between synchronous data (video data), as shown in FIG. 19E, and are transmitted.
Meanwhile, the devices C and D judge transfer data to be received, from the channel number within the packets which are transferred through the P1394 cable 40 to execute receiving of the transfer data. Specifically, the device C receives the transfer data of the ch1, and the device D receives the transfer data of the ch2.
P1394 has the function of automatically setting topology (refer to "Automatic Setting of Topology" on pages 155-159 of Literature 1). P1394 is so arranged as to reset setting of bus upon connection and disconnection of the devices or upon turning-on of a power supply. By resetting of the bus, confirmation of connection relationship among the devices, setting of parentage among the devices, ID setting of each of the devices, and the like are reset.
Such bus resetting operation does not particularly become a problem in a case where the asynchronous data such as computer data are transferred. However, in a case where the image data in which the isochronous transfer is necessary are transferred, the bus resetting operation becomes a problem. Since the isochronous transfer is not assured by the bus resetting, there is also a case where image display stops in a case where, for example, image data are outputted to a monitor so that the image is in the process of being outputted. Moreover, in a case where dubbing recording due to a VTR is executed, if it is considered that the isochronous transfer is not assured, it is necessary to intermittently control the recording of the VTR. In practice, realization of the dubbing recording becomes impossible. Particularly, in domestic equipment, there is a case where connection between a device which has no relation to the data transfer, and the P1394 cable is erroneously cut off during data transmission.
In this manner, there has been the following problem. Specifically, since, continuity of the data before and after the resetting operation is not assured when the bus is reset, data may be lost or problems may occur during transfer of the synchronous data such as image data or the like.
In view of the above, in P1394 the bus resetting is not generated upon connection or disconnection of the devices. However, in synchronous communication such as P1394, the maximum transfer rate in a transmission system is limited. Accordingly, P1394 limits the number of packets which are transferred in the isochronous cycle, in accordance with the maximum transfer rate. Now, it is assumed that transmission of the data is executed between a plurality of devices at a predetermined transfer rate on the basis of such limitation. Here, in a case where another device is newly connected additionally to the P1394 cable, and a synchronous communication signal is transmitted also with respect to the additionally connected device, it is considered that a total transfer rate exceeds a predetermined total transfer rate. At present, P1394 operation in this case is not prescribed. That is, where another device is newly connected, there is the possibility that transmission of all the data also including data presently being transmitted is stopped. Further, when the transfer of the data is permitted, there is also the possibility that data which are sufficiently transmitted during a predetermined isochronous cycle are transmitted during the subsequent isochronous cycle. Thus, there has been a problem that the synchronous transfer is not assured.